The present invention relates to a method for compensating distortion in optical projection and more particularly to a method for producing a distortion-compensated reticle having multiple legends for optical projection on a single screen readout unit.
Film reticles or chips having multiple legends are commonly used for readout on instrument and control panels and are often integrated into keysets. The legends are usually formed in a transparent film matrix and singularly projected to the backside of a single translucent screen by a plurality of separately operated parallel projectors. The projectors are operated according to the legend to be displayed. Due to so-called barrel distortion (pin-cushioning and keystoning) caused by magnification and displacement of the projectors off of the center of the screen, the legends at the reticle must be distorted in order that the projected image will appear undistorted. Various methods for predistorting the legends have been utilized. For example, a single photosensitive film is placed in a camera having plural optical paths from a single objective to separate image areas on the film corresponding to the separate legend areas on the reticle of the readout unit. The separate areas are each exposed one at a time to a desired legend by blanking out all but the corresponding optical path. In this way, the images developed on the film are distorted precisely the amount necessary to compensate for the barrel distortion when projected on corresponding optical paths of a readout unit. Because each legend must be separately photographed on a single film along each optical path, the reticle production is time-consuming and expensive.